Terminal, base station, and communication method

ABSTRACT

Provided is a terminal with which it is possible, in a heterogeneous cell network, to transmit a Periodic-Sounding Reference Signal (P-SRS) at a transmission bandwidth and power density necessary for carrying out both a process of selection of a transceiving participating base station and a process of frequency scheduling of a Physical Uplink Shared Channel (PUSCH). A terminal ( 300 ) comprises a receiving unit ( 301 ) which receives control information which includes information which denotes a P-SRS transmission parameter, and a transmission unit ( 303 ) which, using a transmission parameter which is included in the received control information, transmits a first P-SRS provided with a first bandwidth and a first power density at a first period, and transmits a second P-SRS provided with a second bandwidth which is narrower than the first bandwidth and second power density which is higher than the first power density at a second period.

TECHNICAL FIELD

The present invention relates to a terminal, a base station and acommunication method used in a heterogeneous cell network.

BACKGROUND ART

SC-FDMA (single-carrier frequency-division multiple access) having asmall PAPR (peak-to-average power ratio) and providing high powerutilization efficiency for terminals has been adopted for 3GPP LTE (3rdgeneration partnership project long-term evolution, hereinafter simplyreferred to as “LTE”) uplink. In the LTE uplink, SRSs (soundingreference signals) are used to obtain CSI (channel state information)including various kinds of information such as path loss and channelfrequency response or the like (e.g., see Non-Patent Literature 1).

Each terminal transmits SRSs at periods set beforehand using time andfrequency resources allocated beforehand. A base station measures uplinkCSI based on SRSs periodically received from each terminal in a cell andreferences the CSI of each terminal to thereby perform frequencyscheduling (resource allocation in frequency domain) of a PUSCH(physical uplink shared channel).

A wide-band LTE uplink becomes a frequency selective fading channelwhose gain significantly differs depending on its frequency. Therefore,the base station allocates a PUSCH to a frequency resource having alarge gain, and can thereby maintain high channel quality.

In order for the base station to perform frequency scheduling of aPUSCH, the terminal needs to transmit SRSs in all available bands.

When the terminal is located in the vicinity of the base station, theterminal transmits SRSs having a wide band and small power density. Thebase station can measure wide-band CSI necessary for scheduling of thePUSCH by receiving only one SRS.

On the other hand, when the terminal is located far from the basestation, for example, at a cell edge, a path loss in a propagation pathis large, and power of a signal transmitted from the terminal therebysignificantly attenuates by the time the signal arrives at the basestation. Therefore, in order for the base station to obtain desiredreceiving quality, the terminal is required to increase transmissionpower.

However, transmission power of the terminal has an upper limit andincreasing a power density in a wide band may cause the transmissionpower to exceed the upper limit value. For this reason, the terminalsends SRSs having a large power density in a narrow band (a bandwidthresulting from dividing the whole bandwidth by n, n being an integerequal to or greater than 2) a plurality of times while changing a band(frequency hopping). This allows the base station to receive a pluralityof SRSs, temporally accumulate the SRSs and thereby measure CSI of thewhole bandwidth necessary for PUSCH scheduling.

Note that LTE-Advanced Release 10 (hereinafter, described as “Rel. 10”)which is an evolved version of LTE has introduced A-SRS (aperiodic-SRS)in addition to periodically transmitted SRS (periodic-SRS, hereinafter,referred to as “P-SRS”) (e.g., see Non-Patent Literature 2). An A-SRS istransmitted from the terminal only once in response to a transmissionrequest transmitted from the base station. Since the base station needsto transmit a transmission request to the terminal only when the basestation desires to obtain CSI of a predetermined band, operation withminimized resource consumption is possible in Rel. 10.

In Release 11 which is the next LTE-Advanced version (hereinafter,described as “Rel. 11”), in a heterogeneous cell network (HetNet) asshown in FIG. 1, where there are a plurality of base stations havingdifferent cover areas, studies are being carried out on CoMP(coordinated multi-point) transmission/reception in which a plurality ofbase stations carry out coordinated transmission/reception (e.g., seeNon-Patent Literature 3). HetNet is made up of a macro base station andpico base stations. The macro base station is a base station (node)having large transmission power and coverage, and the pico base stationis a base station (node) having small transmission power and coverage.In Rel. 11 in particular, since a base station located in the vicinityof a terminal can perform reception on the uplink, it is possible toachieve high quality transmission while reducing required transmissionpower in the terminal compared to Rel. 10 or earlier in which only amacro base station exists.

Here, in HetNet, since transmission/reception is performed at multiplepoints located at greatly varying distances, it is necessary toappropriately select a base station that performs transmission/receptionwith a terminal (hereinafter, a base station that carries outtransmission/reception to/from a terminal is called“transmission/reception participating base station”) and also switchbetween transmission/reception participating base stations asappropriate as the terminal moves. Selection of thetransmission/reception participating base station is done by the macrobase station.

Studies are being carried out on the use of reference signals (CRS,CSI-RS, and SRS) transmitted on the uplink and downlink for selectionand switching of transmission/reception participating base stations.When a CRS or CSI-RS transmitted on the downlink is used, the terminalmeasures CSI up to each base station and feeds back the measurementresult using the uplink. The macro base station determines atransmission/reception participating base station based on the fed backCSI. On the other hand, when an SRS transmitted on the uplink is used,the base station can directly measure CSI using the SRS transmitted fromthe terminal. Therefore, it is possible to reduce the amount ofinformation fed back from the terminal to the base station compared to acase where a CRS or CSI-RS is used.

As described above, in Rel. 11 or later in which CoMP is introduced,there is a high possibility that selection of a transmission/receptionparticipating base station using SRSs may be adopted. In this case, anSRS is used for two applications: (1) PUSCH frequency scheduling, and inaddition (2) selection of a transmission/reception participating basestation.

CITATION LIST Non-Patent Literature

NPL 1

-   3GPP TS36.211 v10.1.0 “3GPP TSG RAN; Evolved Universal Terrestrial    Radio Access (E-UTRA); Physical Channels and Modulation”

NPL 2

-   3GPP TS 36.213 V10.1.0, “Physical layer procedures (Release 10),”    March 2011

NPL 3

-   M. Sawahashi, Y. Kishiyama, A. Morimoto, D. Nishikawa, and M. Tanno,    “Coordinated multipoint transmission/reception techniques for    LTE-advanced,” IEEE Wireless Commun., Vol. 17, No. 3, pp. 26-34,    June 2010.

NPL 4

-   R1-080994 LG Electronics, “UL sounding RS Operation,” Feb. 11 to 15,    2008, RAN1 #52

SUMMARY OF INVENTION Technical Problem

In order to select a transmission/reception participating base station,even a base station located far from a terminal needs to be able toreceive SRSs. Therefore, an SRS which has a high power density in anarrow band is suitable for this application. To meet this application,the terminal needs to transmit SRSs at transmission periods at which theterminal can follow switching between base stations as the terminalmoves.

On the other hand, in Rel. 11 or later, since a PUSCH is received by abase station located in the vicinity of a terminal, performing frequencyscheduling of the PUSCH requires only the base station located in thevicinity of the terminal to be able to receive SRSs. Therefore, SRShaving a low power density in a wide band is suitable for thisapplication. To meet this application, the terminal needs to transmitSRSs at transmission periods at which the terminal can follow a channelvariation.

In the Rel. 10 specification, SRSs are not assumed to be used for theabove-described two applications, and SRSs are designed to be used onlyfor frequency scheduling of PUSCHs. For this reason, using SRSs forselection of a transmission/reception participating base stationrequires bandwidth and transmission power to be dynamically changed.

However, dynamically changing bandwidth and transmission power mayresult in a problem that overhead of signaling increases significantly.Hereinafter, this problem will be described in detail.

(Switching of Bandwidth)

In the case of a P-SRS, notification from a higher layer is necessaryfor switching between bandwidths, which involves a considerableswitching delay. Furthermore, frequent switching through notificationfrom a higher layer is not desirable because this would drasticallyincrease overhead.

In the case of an A-SRS, transmission of SRSs having differentbandwidths can be instructed by a transmission request. However, sincean A-SRS of each terminal needs to be one that does not interfere withP-SRSs/A-SRSs transmitted by other terminals, the degree of freedom inthe setting is considerably limited.

(Setting and Change of Transmission Power)

In the specification of Rel. 10 or earlier, transmission power of aP-SRS or A-SRS is set so that the power density becomes constantirrespective of its bandwidth. Therefore, it is not possible to providedifferent power densities for SRSs of different bandwidths.

Closed-loop control using a TPC (transmit power control) command is usedto change transmission power. A TPC command is a command composed of 2bits that instructs to increase/decrease transmission power by apredetermined step width.

To significantly change a power density, the macro base station needs totransmit a plurality of TPC commands to the terminal. In considerationof the fact that power densities of a P-SRS and A-SRS are constantirrespective of their bandwidths, even if SRSs of different bandwidthsare transmitted using a combination of P-SRS and A-SRS, it is necessaryto frequently adjust power using TPC commands in order to set the SRSsto different power densities. Such frequent transmission of TPC commandsmay lead to a great increase in overhead.

As a method using a plurality of types of SRSs having differentbandwidths, one proposed in Non-Patent Literature 4 is known forexample. This method provides a plurality of types of P-SRSs havingdifferent periods, frequency positions and frequency shifts per certainbandwidth, selects one or a plurality of P-SRSs as required, andmultiplexes and transmits the P-SRSs. This method can select P-SRSs in acontinuous band to increase an apparent P-SRS bandwidth or select P-SRSsof different periods to change an apparent P-SRS bandwidth. However, thetechnique described in Non-Patent Literature 4 presents neithertransmission power control for changing a power density nor method forachieving different coverages in one P-SRS set.

An object of the present invention is to provide, in a HetNet, aterminal, a base station and a communication method capable oftransmitting a P-SRS (or A-SRS) at transmission periods necessary toperform processing of both selection of a transmission/receptionparticipating base station and PUSCH frequency scheduling.

Solution to Problem

A terminal according to an aspect of the present invention includes: areceiving section that receives control information includinginformation indicating a transmission parameter of a periodic soundingreference signal (P-SRS); and a transmitting section that transmits afirst P-SRS having a first bandwidth and a first power density at afirst period and transmits a second P-SRS having a second bandwidthnarrower than the first bandwidth and a second power density higher thanthe first power density at a second period, using the transmissionparameter included in the received control information.

A terminal according to an aspect of the present invention includes: areceiving section that receives control information includinginformation indicating a transmission parameter of an aperiodic soundingreference signal (A-SRS); and a transmitting section that transmits afirst A-SRS having a first bandwidth and a first power density during afirst period only when a transmission request is made from a basestation, and transmits a second A-SRS having a second bandwidth narrowerthan the first bandwidth and a second power density higher than thefirst power density during a second period only when a transmissionrequest is made from the base station, using the transmission parameterin the received control information.

A base station according to an aspect of the present invention includes:a transmitting section that transmits control information includinginformation indicating a transmission parameter of a periodic soundingreference signal (P-SRS); a receiving section that receives a firstP-SRS having a first bandwidth and a first power density and a secondP-SRS having a second bandwidth narrower than the first bandwidth and asecond power density higher than the first power density; a measuringsection that measures channel state information (CSI) using the receivedfirst P-SRS and second P-SRS; and a selection section that performsfrequency scheduling using the CSI based on the first P-SRS and thesecond P-SRS and that selects a base station which participates intransmission/reception, using the CSI based on the second P-SRS.

A base station according to an aspect of the present invention includes:a transmitting section that transmits control information includinginformation indicating a transmission parameter of an aperiodic soundingreference signal (A-SRS); a receiving section that receives a firstA-SRS having a first bandwidth and a first power density and a secondA-SRS having a second bandwidth narrower than the first bandwidth and asecond power density higher than the first power density; a measuringsection that measures channel state information (CSI) using the receivedfirst A-SRS and second A-SRS; and a selection section that performsfrequency scheduling using the CSI based on the first A-SRS and thesecond A-SRS, and that selects a base station which participates intransmission/reception, using the CSI based on the second A-SRS.

A communication method according to an aspect of the present inventionincludes: receiving control information including information indicatinga transmission parameter of a periodic sounding reference signal(P-SRS); and transmitting a first P-SRS having a first bandwidth and afirst power density at a first period using the transmission parameterin the received control information; and transmitting a second P-SRShaving a second bandwidth narrower than the first bandwidth and a secondpower density higher than the first power density at a second periodusing the transmission parameter in the received control information.

A communication method according to an aspect of the present inventionincludes: receiving control information including information indicatinga transmission parameter of an aperiodic sounding reference signal(A-SRS); transmitting a first A-SRS having a first bandwidth and a firstpower density during a first period only when a transmission request ismade from a base station, using the transmission parameter in thereceived control information; and transmitting a second A-SRS having asecond bandwidth narrower than the first bandwidth and a second powerdensity higher than the first power density during a second period onlywhen a transmission request is made from the base station, using thetransmission parameter in the received control information.

Advantageous Effects of Invention

According to the present invention, a terminal periodicallytime-division-multiplexes and transmits two types of SRSs: a wide-bandand low power density P-SRS (or A-SRS) and a narrow-band and high powerdensity P-SRS (or A-SRS), based on a transmission parameter indicatedfrom a macro base station, and can thereby transmit the P-SRS (or A-SRS)at a transmission period necessary for performing processing of bothselection of a transmission/reception participating base station andPUSCH frequency scheduling.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram of a cell according to Rel. 11;

FIG. 2 is a block diagram illustrating a configuration of maincomponents of a macro base station according to Embodiment 1 of thepresent invention;

FIG. 3 is a block diagram illustrating a configuration of maincomponents of a pico base station according to Embodiment 1 of thepresent invention;

FIG. 4 is a block diagram illustrating a configuration of maincomponents of a terminal according to Embodiment 1 of the presentinvention;

FIG. 5 is a flowchart illustrating a main processing procedure of eachapparatus according to Embodiment 1 of the present invention;

FIG. 6 illustrates an example of a table listing P-SRS candidatesaccording to Embodiment 1 of the present invention;

FIG. 7 illustrates an example of P-SRSs transmitted from the terminalaccording to Embodiment 1 of the present invention;

FIG. 8 illustrates another example of a table listing P-SRS candidatesaccording to Embodiment 1 of the present invention;

FIG. 9 illustrates a table of SRS bandwidths and frequency hoppingdefined in Rel. 10;

FIG. 10 illustrates a table of SRS period offsets and time offsetsdefined in Rel. 10;

FIG. 11 illustrates another example of P-SRSs transmitted from theterminal according to Embodiment 1 of the present invention;

FIG. 12 illustrates an example of P-SRSs transmitted from a terminal anda transmission power control time according to Embodiment 2 of thepresent invention;

FIG. 13 illustrates another example of P-SRSs transmitted from theterminal and a transmission power control time according to Embodiment 2of the present invention;

FIG. 14 illustrates an example of P-SRSs transmitted from a terminalaccording to another embodiment of the present invention;

FIG. 15 illustrates another example of P-SRSs transmitted from aterminal according to a further embodiment of the present invention;

FIG. 16 is a conceptual diagram of a cell in a heterogeneous networkhaving a two-layer structure;

FIG. 17 illustrates a situation in a case where the present invention isapplied to a heterogeneous network having a two-layer structure;

FIG. 18 illustrates an example of A-SRS transmission resources accordingto Embodiment 3 of the present invention;

FIG. 19 illustrates an example of A-SRSs transmitted from a terminalaccording to Embodiment 3 of the present invention; and

FIG. 20 illustrates an example of A-SRSs transmitted from a terminal anda transmission power control time according to Embodiment 4 of thepresent invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Note that the samecomponents among the embodiments will be assigned the same referencenumerals and detailed description thereof will be omitted.

Embodiment 1

Configuration of Network System

A network system according to Embodiment 1 of the present invention is aHetNet and is made up of macro base station (Macro eNB) 100, pico basestation (Pico eNB) 200, and terminal (UE) 300 as shown in FIG. 1. Onemacro base station 100 and one or a plurality of pico base stations 200are installed in each cell. Macro base station 100 and each pico basestation 200 are connected via a low-delay and large-capacity interfacesuch as an optical fiber. Macro base station 100 and each pico basestation 200 in a cell use an identical cell ID, share a transmissionparameter of SRSs allocated to each terminal 300 located in the cell,receive the SRSs and measure CSI. Each terminal 300 performs radiocommunication with macro base station 100 and/or pico base station 200selected by macro base station 100.

In each terminal 300, a base station that transmits data may bedifferent from a base station that receives data. Macro base station 100can communicate with both terminal 300 a compliant with the Rel. 11specification and terminal 300 b compliant with the specification ofRel. 10 or earlier. In the following description, terminal 300 compliantwith the Rel. 11 specification (terminal 300 a in FIG. 1) will bedescribed.

In the present embodiment, each terminal 300 periodicallytime-division-multiplexes and transmits two types of SRSs: a first P-SRShaving a wide-band and low power density and a second P-SRS having anarrow-band and high power density based on transmission parametersnotified from macro base station 100.

[Configuration of Macro Base Station]

FIG. 2 is a block diagram illustrating a configuration of maincomponents of macro base station 100 according to the presentembodiment. Macro base station 100 shown in FIG. 2 is mainly constructedof receiving section 101, measuring section 102, inter-base-stationinterface (IF) 103, control section 104 and transmitting section 105.

Receiving section 101 performs radio reception processing(down-conversion, demodulation, decoding or the like) on a radio signaltransmitted from each terminal 300 and received via an antenna andextracts a P-SRS, PUSCH, uplink control signal (PUCCH: physical uplinkcontrol channel) or the like. Receiving section 101 outputs the P-SRS tomeasuring section 102. When terminal 300 is located in the vicinity ofmacro base station 100, receiving section 101 extracts both a firstP-SRS and a second P-SRS. On the other hand, when terminal 300 islocated far from macro base station 100, receiving section 101 extractsa second P-SRS.

Measuring section 102 measures CSI using a P-SRS and outputs themeasurement result to control section 104. When terminal 300 is locatedin the vicinity of macro base station 100, measuring section 102measures CSI using the first P-SRS and second P-SRS respectively. On theother hand, when terminal 300 is located far from macro base station100, measuring section 102 measures CSI using the second P-SRS.

Inter-base-station interface 103 carries out wired communication withpico base station 200. More specifically, inter-base-station interface103 transmits information indicating an instruction on participation intransmission/reception to a transmission/reception participating basestation selected by control section 104. Inter-base-station interface103 transmits scheduling information and PUSCH transmission parametersof terminal 300 to pico base station 200 that receives a PUSCH.Inter-base-station interface 103 also receives the CSI measurementresult transmitted from pico base station 200 and transfers the CSImeasurement result to control section 104. Inter-base-station interface103 receives data from terminal 300 transferred from pico base station200.

Control section 104 performs various types of controls such as frequencyscheduling of the PUSCH or selection of a transmission/receptionparticipating base station. More specifically, control section 104selects, as a first P-SRS, a P-SRS having a wide band, low power densityand a transmission period capable of following a channel variation, andselects, as a second P-SRS, a P-SRS having a narrow band, high powerdensity and transmission period capable of following switching betweenbase stations as terminal 300 moves, from among a plurality of P-SRScandidates having mutually different transmission parameters (bandwidth,power offset, period and the presence or absence of frequency hopping).The P-SRS candidates are listed and stored in a table and each P-SRScandidate is assigned a number. Control section 104 transmitsinformation on a number indicating the selected two types of P-SRSs(hereinafter referred to as “P-SRS selection set”) and informationindicating transmission timing of the two types of P-SRSs to terminal300 via transmitting section 105 and transmits the information to eachpico base station 200 via inter-base-station interface 103.

Control section 104 calculates an SINR based on CSI reported from eachpico base station 200 via inter-base-station interface 103 and CSIoutputted from measuring section 102 and selects a base station(transmission/reception participating base station) that participates indownlink transmission or uplink reception based on the SINR. Controlsection 104 then transmits information on the selectedtransmission/reception participating base station to terminal 300 viatransmitting section 105 and transmits the information to each pico basestation 200 via inter-base-station interface 103.

When macro base station 100 itself participates in PUSCH reception,control section 104 performs PUSCH frequency scheduling and determinesPUSCH transmission parameters of terminal 300 based on the CSImeasurement result of the first P-SRS outputted from measuring section102 and the CSI measurement result of the first P-SRS reported from picobase station 200 participating in PUSCH reception via inter-base-stationinterface 103. On the other hand, when macro base station 100 itselfdoes not participate in PUSCH reception, control section 104 performsPUSCH frequency scheduling and determines PUSCH transmission parametersof terminal 300 based on the CSI measurement result of the first P-SRSreported from pico base station 200 participating in PUSCH reception viainter-base-station interface 103. Control section 104 transmitsinformation indicating the PUSCH frequency scheduling result andinformation indicating the PUSCH transmission parameters of terminal 300to terminal 300 via transmitting section 105 and transmits theinformation to pico base station 200 participating in PUSCH receptionvia inter-base-station interface 103.

Note that the CSI measurement result of the second P-SRS may vary underthe influence of channel frequency selectivity. In order to reduce theinfluence, frequency hopping is introduced. Control section 104 canperform successive averaging on CSI measured by second P-SRS in eachpico base station 200. For example, by time-averaging CSI measured everytime one second P-SRS is newly received, it is possible to follow CSIvariations caused by movement of terminal 300 or the like whilepreventing the CSI variations.

Transmitting section 105 performs radio transmission processing (coding,modulation, up-conversion or the like) on a P-SRS selection setoutputted from control section 104 and various kinds of information(information indicating the transmission/reception participating basestation, information indicating the PUSCH scheduling result, informationindicating PUSCH transmission parameters of terminal 300 or the like),PDSCH (physical downlink shared channel), and downlink control signal(PDCCH: physical downlink control channel) or the like and transmits theresultant signal to each terminal 300 via an antenna. The P-SRSselection set may be notified as terminal-specific RRC controlinformation or may be included in the MAC header.

[Configuration of Pico Base Station]

FIG. 3 is a block diagram illustrating a configuration of maincomponents of pico base station 200 according to the present embodiment.Pico base station 200 shown in FIG. 3 is mainly constructed of receivingsection 201, measuring section 202, inter-base-station interface section203, and transmitting section 204.

Receiving section 201 performs radio reception processing on a radiosignal transmitted from each terminal 300 and received via an antenna,extracts a P-SRS and a control signal or the like and outputs the P-SRSto measuring section 202. When instructed from macro base station 100 toparticipate in PUSCH reception, receiving section 201 processes a PUSCHincluded in the received signal according to a PUSCH transmissionparameter of terminal 300 instructed from macro base station 100. Whenterminal 300 is located in the vicinity of pico base station 200,receiving section 201 extracts both a first P-SRS and a second P-SRS. Onthe other hand, when terminal 300 is located far from pico base station200, receiving section 201 extracts a second P-SRS.

Measuring section 202 measures CSI using the P-SRS and transmits themeasurement result to macro base station 100 via inter-base-stationinterface section 203. When terminal 300 is located in the vicinity ofpico base station 200, measuring section 202 measures CSI using thefirst P-SRS and second P-SRS respectively. On the other hand, whenterminal 300 is located far from pico base station 200, measuringsection 202 measures CSI using the second P-SRS.

Inter-base-station interface section 203 carries out wired communicationwith macro base station 100. More specifically, inter-base-stationinterface section 203 receives a P-SRS selection set transmitted frommacro base station 100 and transfers the P-SRS selection set tomeasuring section 202. Inter-base-station interface section 203transmits the CSI measurement result outputted from measuring section202 to macro base station 100. Inter-base-station interface section 203also receives information indicating an instruction on participation intransmission/reception from macro base station 100. When instructed toparticipate in PUSCH reception, inter-base-station interface section 203transmits a PUSCH received from terminal 300 to macro base station 100.

When instructed to participate in PDSCH transmission from macro basestation 100, transmitting section 204 performs radio transmissionprocessing on the PDSCH according to transmission parameters instructedfrom macro base station 100 and transmits the processed signal to eachterminal 300 via an antenna.

[Configuration of Terminal]

FIG. 4 is a block diagram illustrating a configuration of maincomponents of terminal 300 according to the present embodiment. Terminal300 shown in FIG. 4 is mainly constructed of receiving section 301,control section 302 and transmitting section 303.

Receiving section 301 performs radio reception processing on a radiosignal transmitted from macro base station 100 and pico base station 200and received via an antenna, extracts information indicating a P-SRSselection set and a transmission/reception participating base station,information indicating a PUSCH scheduling result, information indicatingPUSCH transmission parameters of terminal 300, PDSCH and downlinkcontrol signal or the like, and outputs information indicating a P-SRSselection set and PUSCH scheduling result, and information indicatingPUSCH transmission parameters of terminal 300 to control section 302.

In accordance with the P-SRS selection set outputted from receivingsection 301, control section 302 instructs transmitting section 303about transmission parameters (bandwidth, power offset, period, and thepresence or absence of frequency hopping) of a first P-SRS and a secondP-SRS. In accordance with information indicating the PUSCH schedulingresult and information on transmission parameters of terminal 300outputted from receiving section 301, control section 302 indicatesPUSCH transmission parameters to transmitting section 303.

Transmitting section 303 performs radio transmission processing on thefirst P-SRS, second P-SRS, PUSCH, uplink control signal or the like andtransmits the processed signal to each terminal 300 via an antenna.Transmitting section 303 performs radio transmission processing on thefirst P-SRS, second P-SRS and PUSCH in accordance with the transmissionparameters indicated from control section 302.

Terminal 300 performs transmission power control on the first P-SRS,second P-SRS and PUSCH. More specifically, terminal 300 first performsopen-loop transmission power control in accordance with a path loss inthe propagation path between base station 100 or 200 which is acommunicating party and terminal 300, and then performs closed-looptransmission power control using a TPC command transmitted from basestation 100 or 200.

[Operation Flow]

Next, a main processing procedure of each apparatus according to thepresent embodiment will be described using FIG. 5.

First, macro base station 100 selects two types of P-SRSs: a first P-SRShaving a wide-band and low power density and a second P-SRS having anarrow band and high power density from among P-SRS candidates describedin a list as shown in FIG. 6. Macro base station 100 transmits, toterminal 300, a P-SRS selection set which is information on numbersindicating the selected two types of P-SRSs (ST501).

Next, terminal 300 sets transmission resources of the first P-SRS andthe second P-SRS based on the P-SRS selection set received from macrobase station 100. Terminal 300 then time-division-multiplexes andtransmits the first P-SRS and second P-SRS to respective base stations100 and 200 according to the set transmission resources (ST502). Forexample, in FIG. 6, when SRS no. 0 is selected as the first P-SRS andSRS no. 5 is selected as the second P-SRS, terminal 300 transmits thefirst P-SRS and the second P-SRS based on transmission parameters (band,transmission timing, and period) as shown in FIG. 7.

Next, respective base stations 100 and 200 measure CSIs using thereceived P-SRSs. Macro base station 100 then performs PUSCH frequencyscheduling and determines transmission parameters based on the CSIsmeasured in respective base stations 100 and 200. Macro base station 100also calculates an SINR based on the CSI measured in respective basestations 100 and 200 and selects a transmission/reception participatingbase station based on the SINR. Macro base station 100 then notifiesterminal 300 and each pico base station 200 of information indicatingthe selected transmission/reception participating base station. Macrobase station 100 further notifies terminal 300 and pico base station 200participating in PUSCH reception of PUSCH frequency scheduling and PUSCHtransmission parameters (ST503).

Next, terminal 300 transmits a PUSCH based on the notified PUSCHtransmission parameters (ST504).

Macro base station 100 continues monitoring CSI measurement results ofrespective base stations 100 and 200, switches thetransmission/reception participating base station and changes frequencyresources for PUSCH scheduling in accordance with a change in the CSImeasurement results.

[Effects]

As described above, in the present embodiment, terminal 300time-division-multiplexes and transmits two types of SRSs: a first P-SRShaving a wide-band and low power density and a second P-SRS having anarrow-band and high power density based on the transmission parametersnotified from macro base station 100. This makes it possible to transmitP-SRSs at transmission periods necessary to perform processing of bothselection of a transmission/reception participating base station andPUSCH frequency scheduling.

[Variation 1]

In the present embodiment, as shown in FIG. 8, a combination of P-SRScandidates which is likely to be selected as a pair of the first P-SRSand second P-SRS or a combination of P-SRS candidates which has a higheffect of being selected as a pair of the first P-SRS and second P-SRSmay be selected beforehand. In this case, instead of assigning a numberto each P-SRS candidate, a number may be assigned to each combination ofP-SRS candidates (“Set. No” in FIG. 8).

In this case, it is possible to reduce overhead necessary for macro basestation 100 to notify terminal 300 of the selected P-SRS.

[Variation 2]

Note that the bandwidth, period, frequency hopping pattern or the likeof an SRS are already defined in the Rel. 10 specification. Thus, in thepresent embodiment, instead of creating a new table, macro base station100 may select two types of P-SRSs from an already existing SRS list ofRel. 10. For example, macro base station 100 selects two types of P-SRSswhich do not collide with each other from tables in FIG. 9 and FIG. 10.In this case, however, power offset information for differentiatingcoverage of the two types of P-SRSs needs to be separately notified fromterminal-specific RRC control information or the MAC header or the like.

In this case, since the P-SRSs to be transmitted are a combination ofP-SRSs used by a terminal of Rel. 10 or earlier with a power offset, itis possible to easily realize coexistence (orthogonal multiplexing) witha terminal of Rel. 10 or earlier.

[Variation 3] In the present embodiment, terminal 300 may determinepower offsets of two types of P-SRSs based on the following equation.

$\begin{matrix}{\left( {{Equation}\mspace{14mu} 1} \right)\mspace{619mu}} & \; \\{{{P_{{W - {SRS}},c}(i)} = {\min{\begin{Bmatrix}{{P_{{CMAX},c}(i)},} \\\begin{matrix}{{P_{{SRS\_ OFFSET},c}(i)} + {10\;\log_{10}\left( M_{{W - {SRS}},c} \right)} +} \\{{P_{{O\_ PUSCH},c}(j)} + {{\alpha_{c}(j)} \cdot {PL}_{c}} + {f_{c}(i)}}\end{matrix}\end{Bmatrix}\mspace{14mu}\lbrack{dBm}\rbrack}}}{{P_{{N - {SRS}},c}(i)} = {{P_{{W - {SRS}},c}(i)}\mspace{14mu}\lbrack{dBm}\rbrack}}} & \lbrack 1\rbrack\end{matrix}$

In equation 1 above, P_(W-SRS,c) (i) is transmission power of the firstP-SRS and is the same as the power equation defined in Rel. 10.P_(N-SRS,c) (i) is transmission power of the second P-SRS. Equation 1above expresses that the transmission power of the first P-SRS isdefined based on the power equation of Rel. 10 and the second P-SRS isassumed to have the same transmission power with reference to this.Transmission power is given by bandwidth×power density. Therefore, forexample, when the bandwidth of the second P-SRS is ¼ of that of thefirst P-SRS, the power density of the second P-SRS is four times that ofthe first P-SRS.

In this case, terminal 300 can transmit two types of P-SRSs havingdifferent bandwidths and power densities and form two differentcoverages without notifying terminal 300 of the power offsets from macrobase station 100.

[Variation 4]

In the present embodiment, terminal 300 may periodically stoptransmission of some of the first P-SRSs as shown in FIG. 11 andtransmit the second P-SRSs instead. In this case, the P-SRS transmissionperiod can be kept constant.

Embodiment 2

Embodiment 2 will describe a case where closed-loop transmission powercontrol is respectively performed on two types of P-SRSs transmitted byterminal 300. A configuration of a network system in Embodiment 2 is thesame as that in Embodiment 1. In Embodiment 2, main configurations ofmacro base station 100, pico base station 200, and terminal 300 are thesame as those in Embodiment 1. Embodiment 2 is different from Embodiment1 in respective functions of control section 104 and transmittingsection 105 of macro base station 100, and receiving section 301 andcontrol section 302 of terminal 300.

[Additional Function of Macro Base Station]

In the present embodiment, control section 104 of macro base station 100performs the processing described in Embodiment 1, and further generatesa TPC command (2 bits) of a downlink control signal (PDCCH) based on acomparison in magnitude between a target SINR and an SINR of a receivedP-SRS and outputs the TPC command to transmitting section 105. Controlsection 104 outputs a PDCCH to transmitting section 105 and controlstransmitting section 105 so that the TPC command is transmitted attiming applied to a desired P-SRS.

Transmitting section 105 performs the processing described in Embodiment1 and further transmits a PDCCH including a TPC command based on aninstruction from control section 104.

In the present embodiment, a signal to which a TPC command is appliedchanges in accordance with a time during which macro base station 100transmits the TPC command. The relationship between the transmissiontime of the TPC command and the signal to which the TPC command isapplied is determined between macro base station 100 and terminal 300.

In an example of FIG. 12, only a TPC command transmitted from macro basestation 100 during time 601 between a transmission timing of a firstP-SRS transmitted immediately before a second P-SRS and a transmissiontiming of a second P-SRS is applied to closed-loop control of the secondP-SRS, and a TPC command transmitted from macro base station 100 duringother time 602 is applied to closed-loop control of the first P-SRS andPUSCH.

[Additional Function of Terminal]

Receiving section 301 of terminal 300 performs the processing describedin Embodiment 1, and further extracts a PDCCH including a TPC commandfrom the received signal and outputs the TPC command to control section302.

Control section 302 performs the processing described in Embodiment 1.Control section 302 monitors timings at which receiving section 301receives a PDCCH and determines a target signal to which a TPC commandincluded in the PDCCH is applied. Control section 302 then performs thetransmission power control instructed by the TPC command on the targetsignal to which the TPC command is applied.

[Effects]

In addition to the effects of Embodiment 1, the present embodimentachieves an effect of being able to independently perform a plurality oftypes of closed-loop power controls while minimizing the expansion ofTPC commands. For example, according to the present embodiment, a TPCcommand of Rel. 10 can also be used as is. Of a first P-SRS, a secondP-SRS and a PUSCH, the second P-SRS is a signal intended to be receivedat base station 100 or 200 located far from terminal 300, and the firstP-SRS and PUSCH are signals intended to be received at base station 100or 200 located in the vicinity of terminal 300. Therefore, in thepresent embodiment, two mutually independent types of controls:closed-loop control of the second P-SRS and closed-loop control oflinking both the first P-SRS and PUSCH may be performed as shown in FIG.12. In the present embodiment, signals to which a TPC command is appliedcan be weighted by changing a combination of periods of two types ofP-SRSs. In the example of FIG. 12, time 602 during which the TPC commandis applied to the first P-SRS and PUSCH is seven times as long as time601 during which the TPC command is applied to the second P-SRS.

[Variation 1]

In the present embodiment, signals to which a TPC command is applied canalso be switched by a frequency resource (search space) to which a PDCCHincluding a TPC command is mapped. In this case, a plurality of types ofcontrols can be performed without causing any temporal constraints.

[Variation 2]

In the present embodiment, it is possible to introduce closed-loopcontrols, and then provide a plurality of frequency resources to which aPDCCH is mapped, and switch between the types of controls in accordancewith a time during which a PDCCH including a TPC command istransmitted/received and a frequency resource by which a PDCCH includinga TPC command is transmitted/received. In addition, differences as beingsuperior or inferior to each other may be set in time and frequency. Forexample, signals to which a TPC command is applied are normally switchedusing time division in the same way as in FIG. 12. However, for time 601during which the TPC command is applied to the second P-SRS, only whenpower of the first P-SRS and PUSCH is adjusted, a control signalincluding the TPC command is mapped to a position of a specificfrequency resource (search space). That is, during time 601, a controlsignal for adjusting power of the second P-SRS and a control signal foradjusting power of the first P-SRS and PUSCH may be multiplexed on afrequency resource and may be transmitted temporally at the same time.For example, as shown in FIG. 13, for time 601 during which a TPCcommand is applied to the second P-SRS, a control signal including theTPC command is mapped to position B of the frequency resource only whenpower of the first P-SRS and PUSCH is adjusted. Thus, for time 601during which a TPC command is applied to the second P-SRS, a controlsignal for adjusting power of the second P-SRS mapped to position A ofthe frequency resource and a control signal for adjusting power of thefirst P-SRS and PUSCH mapped to position B of the frequency resource aremultiplexed on the frequency resource and transmitted temporally at thesame time. This indicates a case where a control signal is mapped to aspecific frequency resource only when driven out of necessity whilegiving priority to switching between signals to which a TPC command isapplied using time division.

[Variation 3]

For terminal 300 which has sufficiently high quality of connection withbase station 100 or 200 and has a moderate CSI variation, base station100 can sufficiently perform processing of both selection of atransmission/reception participating base station and PUSCH frequencyscheduling if only base station 100 can receive a first P-SRS. For suchterminal 300, in Embodiments 1 and 2 above, the present invention maystop transmission of the second P-SRS only when terminal 300 receives atransmission request for a specific A-SRS (hereinafter, referred to as“A-SRS trigger”) at a specific timing.

For example, as shown in FIG. 14, when terminal 300 receives an A-SRStrigger which instructs that an A-SRS having the same bandwidth as thatof the second P-SRS currently being transmitted should be transmitted atthe same timing as the second P-SRS, terminal 300 stops transmission ofthe second P-SRS thereafter.

Alternatively as shown in FIG. 15, when terminal 300 receives theabove-described A-SRS trigger, terminal 300 stops transmission of thesecond P-SRS only at that timing.

In this way, when there is a shortage of SRS resources such as when thenumber of terminals increases drastically or when A-SRSs are desired tobe transmitted to many terminals, second P-SRS resources can bereleased, making it possible to solve the problem of the shortage ofresources.

[Variation 4]

The present invention is also applicable to a case where macro basestation 100 and pico base station 200 form cells with mutually differentcell IDs. In this case, aside from specific cell IDs, a common cell ID(also referred to as “virtual cell ID”) commonly defined for all basestations in the same cell is defined for macro base station 100 and picobase station 200 (FIG. 16). SRSs using a base sequence and hoppingpattern generated with a specific cell ID are not orthogonal to eachother and cause interferences. On the other hand, SRSs using a basesequence and hopping pattern generated with a common cell ID can beeasily made orthogonal to each other among all base stations in thecell.

In a heterogeneous network having a two-layer structure, terminal 300 inthe present embodiment generates first P-SRSs using a base sequence andhopping pattern generated with a specific cell ID and generates secondP-SRSs using a base sequence and hopping pattern generated with a commoncell ID.

As in the case of the conventional heterogeneous network, first P-SRSsand PUSCHs can be used for measurement by only base stations 100 and 200connected (base station with cell ID #5 in the example of FIG. 17). Onthe other hand, second P-SRSs can also be made orthogonal to each otherby peripheral base stations 100 and 200, and can be used for measurementwith high accuracy without causing interference. Therefore, it ispossible to realize smooth handover.

Embodiment 3

A case has been described in Embodiments 1 and 2 above where terminal300 time-division-multiplexes and transmits two types of SRSs: a firstP-SRS having a wide-band and low power density and a second P-SRS havinga narrow-band and high power density based on transmission parametersnotified from macro base station 100.

A case will be described in Embodiment 3 where terminal 300time-division-multiplexes and transmits two types of SRSs: a first A-SRShaving a wide-band and low power density and a second A-SRS having anarrow-band and high power density based on transmission parametersnotified from macro base station 100. A configuration of a networksystem in Embodiment 3 is the same as that of Embodiment 1. Mainconfigurations of macro base station 100, pico base station 200 andterminal 300 in Embodiment 3 are the same as those of Embodiment 1.Embodiment 3 is different from Embodiment 1 in respective functions ofreceiving section 101, measuring section 102, control section 104 andtransmitting section 105 of macro base station 100, receiving section201 and measuring section 202 of pico base station 200, and receivingsection 301, control section 302 and transmitting section 303 ofterminal 300.

[Additional Functions of Macro Base Station]

Compared to the processing described in Embodiment 1, receiving section101 performs A-SRS extraction processing instead of P-SRS extractionprocessing. Receiving section 101 outputs A-SRSs to measuring section102. When terminal 300 is located in the vicinity of macro base station100, receiving section 101 extracts both a first A-SRS and a secondA-SRS. On the other hand, when terminal 300 is located far from macrobase station 100, receiving section 101 extracts a second A-SRS.

Measuring section 102 measures CSI using an A-SRS and outputs themeasurement result to control section 104. When terminal 300 is locatedin the vicinity of macro base station 100, measuring section 102measures CSI using the first A-SRS and second A-SRS respectively. On theother hand, when terminal 300 is located far from macro base station100, measuring section 102 measures CSI using the second A-SRS.

Compared to the processing described in Embodiment 1, control section104 performs processing of selecting a first A-SRS and second A-SRSinstead of processing of selecting a first P-SRS and second P-SRS. Morespecifically, control section 104 selects, as a first A-SRS, an A-SRShaving a wide-band, low power density and a transmission period capableof following a channel variation, and selects, as a second A-SRS, anA-SRS having a narrow-band, high power density and a transmission periodcapable of following switching between base stations as terminal 300moves, from among a plurality of A-SRS candidates having mutuallydifferent transmission parameters (bandwidth, frequency position, poweroffset, period and timing). Control section 104 then transmitsinformation indicating transmission parameters of a plurality of A-SRSsincluding the first A-SRS and second A-SRS (hereinafter, referred to as“A-SRS parameter set”) to terminal 300 via transmitting section 105 andtransmits the information to each pico base station 200 viainter-base-station interface 103. The A-SRS transmission parameters maybe the same as or different from the P-SRS transmission parameters.

When macro base station 100 itself participates in PUSCH reception,control section 104 performs PUSCH frequency scheduling and determinesPUSCH transmission parameters of terminal 300 based on the CSImeasurement result of the first A-SRS outputted from measuring section102 and the CSI measurement result of the first A-SRS reported from picobase station 200 participating in PUSCH reception via inter-base-stationinterface section 103. When macro base station 100 itself does notparticipate in PUSCH reception, control section 104 performs PUSCHfrequency scheduling and determines PUSCH transmission parameters ofterminal 300 based on the CSI measurement result of the first A-SRSreported from pico base station 200 participating in PUSCH reception viainter-base-station interface section 103. Control section 104 transmitsinformation indicating the PUSCH frequency scheduling result andinformation indicating the PUSCH transmission parameters of terminal 300to terminal 300 via transmitting section 105 and transmits theinformation to pico base station 200 participating in PUSCH receptionvia inter-base-station interface section 103.

Compared to the processing described in Embodiment 1, transmittingsection 105 performs radio transmission processing (coding, modulation,up-conversion or the like) on an A-SRS parameter set instead of a P-SRSselection set, and transmits the processed A-SRS parameter set to eachterminal 300 via an antenna. Note that the A-SRS parameter set may benotified as terminal-specific RRC control information or may be includedin the MAC header. Transmitting section 105 determines. for eachindividual terminal, whether or not to request A-SRS transmission at thenext timing when A-SRS transmission is possible, and transmits 1-bit or2-bit A-SRS trigger included in a PDCCH.

[Additional Function of Pico Base Station]

Compared to the processing described in Embodiment 1, receiving section201 performs A-SRS extraction processing instead of P-SRS extractionprocessing. Receiving section 201 outputs an A-SRS to measuring section202. When terminal 300 is located in the vicinity of pico base station200, receiving section 201 extracts both a first A-SRS and a secondA-SRS. On the other hand, when terminal 300 is located far from picobase station 200, receiving section 201 extracts a second A-SRS.

Measuring section 202 measures CSI using the A-SRS and transmits themeasurement result to macro base station 100 via inter-base-stationinterface section 203. When terminal 300 is located in the vicinity ofpico base station 200, measuring section 202 measures CSI using thefirst A-SRS and second A-SRS respectively. On the other hand, whenterminal 300 is located far from pico base station 200, measuringsection 202 measures CSI using the second A-SRS.

[Additional Function of Terminal]

Compared to the processing described in Embodiment 1, receiving section301 performs processing of extracting an A-SRS parameter set instead ofprocessing of extracting a P-SRS selection set. Receiving section 301outputs the extracted A-SRS parameter set to control section 302.Receiving section 301 detects an A-SRS trigger from a PDCCH and outputsthe A-SRS trigger to control section 302.

In accordance with the A-SRS parameter set outputted from receivingsection 301, control section 302 instructs transmitting section 303about transmission parameters (bandwidth, frequency position, poweroffset, period and timing) of a first A-SRS and a second A-SRS. Controlsection 302 instructs transmitting section 303 to transmit the firstA-SRS or second A-SRS in accordance with the A-SRS trigger outputtedfrom receiving section 301.

Compared to the processing described in Embodiment 1, transmittingsection 303 performs radio transmission processing on the first A-SRSand second A-SRS instead of radio transmission processing on the firstP-SRS and second P-SRS. More specifically, upon receiving an instructionfor transmitting the first A-SRS or second A-SRS from control section302, transmitting section 303 performs radio transmission processing onthe A-SRS at transmittable timing closest to a point in time apredetermined time (e.g., 4 ms) after the A-SRS trigger is detected as astarting point.

Compared to the processing described in Embodiment 1, terminal 300performs transmission power control on the first A-SRS and second A-SRSinstead of transmission power control on the first P-SRS and secondP-SRS.

[Operation Flow]

Next, a main processing procedure of each apparatus according to theprocessing in the present embodiment will be described.

First, macro base station 100 selects a first A-SRS having a wide-bandand low power density and a second A-SRS having a narrow-band and highpower density. Macro base station 100 then transmits, to terminal 300,an A-SRS parameter set which is information indicating a plurality ofA-SRS transmission parameters including the selected two types ofA-SRSs.

Next, terminal 300 sets beforehand, transmission resources of the firstA-SRS and second A-SRS based on the A-SRS parameter set received frommacro base station 100. FIG. 18 illustrates an example of A-SRStransmission resources set beforehand.

Macro base station 100 includes an A-SRS trigger in a PDCCH as necessaryand transmits it to terminal 300.

Upon receiving the A-SRS trigger, terminal 300 transmits the first A-SRSor second A-SRS to each base station 100 or 200 using the transmissionresource closest to a point in time a predetermined time (e.g., 4 ms)after the A-SRS trigger is detected among A-SRS transmission resourcesset beforehand as a starting point. FIG. 19 illustrates an example ofA-SRSs transmitted from the terminal according to present Embodiment 3.FIG. 19 illustrates a situation in which the first A-SRS and secondA-SRS are respectively transmitted a plurality of times according toA-SRS triggers. The first A-SRS and second A-SRS are transmitted only atpredetermined respective periods and timings. Therefore, the first A-SRSand second A-SRS are not transmitted redundantly.

Next, each base station 100 or 200 measures CSI using the receivedA-SRSs. Macro base station 100 then performs PUSCH frequency schedulingand determines transmission parameters based on the CSI measured in eachbase station 100 or 200. Macro base station 100 calculates an SINR basedon the CSI measured in each base station 100 or 200 and selects atransmission/reception participating base station based on the SINR.Macro base station 100 then notifies terminal 300 and each pico basestation 200 of information indicating the selectedtransmission/reception participating base station. Macro base station100 further notifies terminal 300 and pico base station 200participating in PUSCH reception of PUSCH frequency scheduling and PUSCHtransmission parameters.

Next, terminal 300 transmits a PUSCH based on the notified PUSCHtransmission parameters.

Macro base station 100 continues monitoring CSI measurement results ofeach base station 100 or 200, switches between transmission/receptionparticipating base stations and changes frequency resources for PUSCHscheduling in accordance with the change in the CSI measurement results.

[Effects]

As described above, in the present embodiment, terminal 300time-division-multiplexes and transmits two types of SRSs: a first A-SRShaving a wide-band and low power density and a second A-SRS having anarrow-band and high power density based on transmission parametersnotified from macro base station 100. It is thereby possible to obtaineffects similar to those of Embodiment 1. In the present embodiment,since the first A-SRS or second A-SRS is transmitted only when terminal300 receives an A-SRS trigger, no SRS is transmitted when each basestation 100 or 200 does not need any SRSs. This reduces powerconsumption of terminal 300 and interference provided to other cells. Inthe present embodiment, since macro base station 100 can select an A-SRSto be transmitted to terminal 300 through an A-SRS trigger, it ispossible to freely change the transmission ratio between the first A-SRSand second A-SRS without changing the setting of A-SRS transmissionparameters.

[Variation 1]

In the present embodiment, as in the case of variation 4 of Embodiment 2above, terminal 300 may generate a first A-SRS using a base sequence andhopping pattern generated with a specific cell ID and generate a secondA-SRS using a base sequence and hopping pattern generated with a commoncell ID.

This allows only base stations 100 and 200 located in the vicinity ofterminal 300 to use the first A-SRS for measurement. On the other hand,since the second A-SRS can be easily orthogonalized in all base stations100 and 200 in the cell, all base stations 100 and 200 can performmeasurement with high accuracy using the second A-SRS. Therefore, smoothhandover and A-SRS orthogonalization over a wide area can be realized.

[Variation 2]

In the present embodiment, contrary to variation 1, terminal 300 maygenerate a first A-SRS using a base sequence and hopping patterngenerated with a common cell ID and generate a second A-SRS using a basesequence and hopping pattern generated with a specific cell ID.

When the second A-SRS is generated with a different cell ID, each basestation 100 or 200 cannot separate the second A-SRS. However, in asituation in which the number of terminals exceeds the capacity of A-SRSorthogonality, generating A-SRSs with different cell IDs rather thangenerating A-SRSs with a single cell ID can randomize and thereby reduceinterference. Therefore, in a situation in which the number of terminalsis quite large and there is a shortage in the capacity of A-SRSorthogonality, it is possible to randomize interference of A-SRSs over awide area.

[Variation 3]

In the present embodiment, preset frequency hopping of A-SRStransmission resources may be performed. That is, frequency positions ofA-SRS transmission resources may be caused to hop according to a presetpattern, and, when an A-SRS trigger is received, A-SRSs may betransmitted at frequency positions determined by the hopping.

In this way, CSI can be measured over a wide band even with a secondA-SRS, that is, a narrow band A-SRS, by triggering it a plurality oftimes, and, thereby, even base stations 100 and 200 located far fromterminal 300 can thereby obtain wide-band and high accuracy CSI.

Embodiment 4

A case will be described in Embodiment 4 where closed-loop transmissionpower control is respectively performed on two types of A-SRSstransmitted by terminal 300. A configuration of a network system inEmbodiment 4 is the same as that in Embodiment 3. In Embodiment 4, mainconfigurations of macro base station 100, pico base station 200, andterminal 300 are the same as those of Embodiment 3. Embodiment 4 isdifferent from Embodiment 3 in respective functions of control section104 and transmitting section 105 of macro base station 100 and receivingsection 301 and control section 302 of terminal 300.

[Additional Function of Macro Base Station]

In the present embodiment, control section 104 of macro base station 100performs the processing described in Embodiment 3, and further generatesa TPC command (2 bits) of a downlink control signal (PDCCH) based on acomparison in magnitude between a target SINR and an SINR of a receivedA-SRS and outputs the TPC command to transmitting section 105. Controlsection 104 outputs a PDCCH to transmitting section 105 and controlstransmitting section 105 so that the TPC command is transmitted attiming applied to a desired A-SRS.

Transmitting section 105 performs the processing described in Embodiment3, and further transmits a PDCCH including a TPC command based on aninstruction from control section 104.

In the present embodiment, a signal to which a TPC command is appliedchanges in accordance with a time during which macro base station 100transmits the TPC command. The relationship between the transmissiontime of the TPC command and the signal to which the TPC command isapplied is predetermined between macro base station 100 and terminal300.

In an example of FIG. 20, only a TPC command transmitted from macro basestation 100 during time 1001 between a transmission timing of a firstA-SRS transmitted immediately before a second A-SRS and a transmissiontiming of a second A-SRS is applied to closed-loop control of the secondA-SRS, and a TPC command transmitted from macro base station 100 duringother time 1002 is applied to closed-loop control of the first A-SRS andPUSCH.

[Additional Function of Terminal]

Receiving section 301 of terminal 300 performs the processing describedin Embodiment 3, and further extracts a PDCCH including a TPC commandfrom the received signal and outputs the TPC command to control section302.

Control section 302 performs the processing described in Embodiment 3,and further monitors timings at which receiving section 301 receives aPDCCH and determines a target signal to which a TPC command included inthe PDCCH is applied. Control section 302 then performs the transmissionpower control instructed by the TPC command on the target signal towhich the TPC command is applied.

[Effects]

In addition to the effects of Embodiment 3, the present embodimentachieves an effect of being able to independently perform a plurality oftypes of closed-loop power controls while minimizing the expansion ofTPC commands. For example, according to the present embodiment, TPCcommands of Rel. 10 can be used as they are. Of a first A-SRS, a secondA-SRS, and a PUSCH, the second A-SRS is a signal intended for receptionat base station 100 or 200 located far from terminal 300, and the firstA-SRS and PUSCH are signals intended for reception at base station 100or 200 located in the vicinity of terminal 300. Therefore, in thepresent embodiment, two mutually independent types of controls:closed-loop control linking both the first A-SRS and PUSCH andclosed-loop control of the second A-SRS may be performed. Furthermore,in the present embodiment, signals to which a TPC command is applied canbe weighted by changing a combination of periods of two types of A-SRSs.In the example of FIG. 20, time 1002 during which a TPC command isapplied to the first A-SRS and PUSCH is seven times as long as time 1001during which a TPC command is applied to the second A-SRS.

[Variation 1]

In the present embodiment, signals to which a TPC command is applied mayalso be switched by frequency resources (search spaces) to which a PDCCHincluding a TPC command is mapped. In this case, a plurality of types ofcontrols can be performed without causing any temporal constraint.

[Variation 2]

In the present embodiment, it is possible to introduce closed-loopcontrols, and then provide a plurality of frequency resources to which aPDCCH is mapped, and switch between the types of controls in accordancewith a time during which a PDCCH including a TPC command istransmitted/received and a frequency resource by which a PDCCH includinga TPC command is transmitted/received. In this case, differences asbeing superior or inferior to each other may be set in time andfrequency.

[Variation 3]

In the present embodiment, only when an A-SRS trigger is transmitted,closed-loop control may be applied to a A-SRS to which the trigger isapplicable. That is, only TPC commands of PDCCHs instructingtransmission of respective A-SRS triggers are applied to A-SRSclosed-loop control.

When A-SRSs are not transmitted, it is thereby possible to preventunnecessary transmission power control from being performed on theA-SRSs.

[Variation 4]

A rule for setting signals to which TPC commands are applied in thepresent embodiment and variations 1 to 3 may be a rule predetermined ina base station and terminal or a system, or a rule selected by a basestation from among a plurality of rules, and notified to respectiveterminals and thereby applied to a system.

This allows conditions for applying TPC commands to be changed inaccordance with the arrangement of a base station, distribution ofterminals, traffic and interference conditions.

(1) Although the embodiments have been described above with an antennaas an example, the present invention can be applied to an antenna portin the same manner.

The term “antenna port” refers to a logical antenna including one ormore physical antennas. In other words, the term “antenna port” does notnecessarily refer to a single physical antenna and may sometimes referto an antenna array including a plurality of antennas, and/or the like.

For example, how many physical antennas are included in the antenna portis not defined in LTE, but the antenna port is defined as a minimum unitallowing the base station to transmit a different reference signal inLTE.

In addition, an antenna port may be defined as a minimum unit formultiplication of a precoding vector weighting.

(2) In the embodiments described above, the present invention isconfigured with hardware by way of example, but the invention may alsobe provided by software in cooperation with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

The disclosures of Japanese Patent Applications No. 2011-219540, filedon Oct. 3, 2011, and No. 2012-108449, filed on May 10, 2012, includingthe specifications, drawings and abstracts are incorporated herein byreference in their entirety.

INDUSTRIAL APPLICABILITY

The present invention is useful as a terminal, a base station and acommunication method capable of performing processing of both selectionof a transmission/reception participating base station and PUSCHfrequency scheduling, using SRSs in HetNet.

REFERENCE SIGNS LIST

-   -   100 Macro base station    -   101 Receiving section    -   102 Measuring section    -   103 Inter-base-station interface section    -   104 Control section    -   105 Transmitting section    -   200 Pico base station    -   201 Receiving section    -   202 Measuring section    -   203 Inter-base-station interface section    -   204 Transmitting section    -   300 Terminal    -   301 Receiving section    -   302 Control section    -   303 Transmitting section

The invention claimed is:
 1. A base station comprising: a transmitter,which, in operation, transmits control information in a PhysicalDownlink Control Channel (PDCCH) to a terminal apparatus, the controlinformation including a transmission request for an aperiodic soundingreference signal (A-SRS) and a transmission power control command (TPCcommand), a receiver, which, in operation, receives the A-SRS from theterminal apparatus, and control circuitry, which, in operation, measureschannel state information (CSI) based on the received A-SRS, wherein,the receiver, in operation, receives a first A-SRS at a firsttransmission power value, and, in response to the transmittertransmitting a request for a second A-SRS, receives the second A-SRS ata second transmission power value; the first transmission power value iscontrolled at the terminal apparatus using one or more first TPCcommands received in a first time period; and the second transmissionpower value is controlled at the terminal apparatus using one or moresecond TPC commands received in a second time period which is other thanthe first time period, follows the first time period, and has adifferent time length than the first time period.
 2. The base stationaccording to claim 1, wherein the first transmission power value of thefirst A-SRS is controlled at the terminal apparatus using the first TPCcommands received within a first band, and the second transmission powervalue of the second A-SRS is controlled at the terminal apparatus usingthe second TPC commands received within a second band which is differentfrom the first band.
 3. The base station according to claim 1, whereinthe relationship between transmission timing of the first TPC commandsand transmission timing of the first A-SRS is predetermined.
 4. The basestation according to claim 1, wherein the first transmission power valueof the first A-SRS is controlled at the terminal apparatus independentlyof transmission power control of a Physical Uplink Shared Channel(PUSCH).
 5. A communication method performed by a base station, themethod comprising: transmitting control information in a PhysicalDownlink Control Channel (PDCCH) to a terminal apparatus, the controlinformation including a transmission request for an aperiodic soundingreference signal (A-SRS) and a transmission power control command (TPCcommand), receiving the A-SRS from the terminal apparatus, and measuringchannel state information (CSI) based on the received A-SRS, wherein thereceiving of the A-SRS from the terminal apparatus includes: receiving afirst A-SRS at a first transmission power value, which is controlled atthe terminal apparatus using one or more first TPC commands received ina first time period, and receiving a second A-SRS at a secondtransmission power value, which is controlled at the terminal apparatususing one or more second TPC commands received in a second time periodwhich is other than the first time period, follows the first timeperiod, and has a different time length than the first time period. 6.The communication method according to claim 5, wherein the firsttransmission power value of the first A-SRS is controlled at theterminal apparatus using the first TPC commands received within a firstband, and the second transmission power value of the second A-SRS iscontrolled at the terminal apparatus using the second TPC commandsreceived within a second band different from the first band.
 7. Thecommunication method according to claim 5, wherein the relationshipbetween transmission timing of the first TPC commands and transmissiontiming of the first A-SRS is predetermined.
 8. The communication methodaccording to claim 5, wherein the first transmission power value of thefirst A-SRS is controlled at the terminal apparatus independently oftransmission power control of a Physical Uplink Shared Channel (PUSCH).9. The communication method according to claim 5, wherein the firstA-SRS is received in response to the base station transmitting a requestfor the first A-SRS to the terminal apparatus.
 10. The communicationmethod according to claim 5, wherein the second A-SRS is received inresponse to the base station transmitting a request for the second A-SRSto the terminal apparatus.
 11. An integrated circuit that controls aprocess performed at a base station apparatus, the integrated circuitcomprising: circuitry which, in operation, controls transmission ofcontrol information in a Physical Downlink Control Channel (PDCCH) to aterminal apparatus, the control information including a transmissionrequest for an aperiodic sounding reference signal (A-SRS) and atransmission power control command (TPC command), and an input, which iscoupled to the circuitry and which, in operation, receives the A-SRSfrom the terminal apparatus, wherein the circuitry, in operation,measures channel state information (CSI) based on the received A-SRSreceived via the input, and wherein the input, in operation, receives afirst A-SRS at a first transmission power value, which is controlled atthe terminal apparatus using one or more first TPC commands received ina first time period, and receives a second A-SRS at a secondtransmission power value, which is controlled at the terminal apparatususing one or more second TPC commands received in a second time periodwhich is other than the first time period, follows the first timeperiod, and has a different time length than the first time period. 12.The integrated circuit according to claim 11, wherein the firsttransmission power value of the first A-SRS is controlled at theterminal apparatus using the first TPC commands received within a firstband, and the second transmission power value of the second A-SRS iscontrolled at the terminal apparatus using the second TPC commandsreceived within a second band which is different from the first band.13. The integrated circuit according to claim 11, wherein therelationship between transmission timing of the first TPC commands andtransmission timing of the first A-SRS is predetermined.
 14. Theintegrated circuit according to claim 11, wherein the first transmissionpower value of the first A-SRS is controlled at the terminal apparatusindependently of transmission power control of a Physical Uplink SharedChannel (PUSCH).
 15. The integrated circuit according to claim 11,wherein the first A-SRS is received in response to the base stationtransmitting a request for the first A-SRS to the terminal apparatus.16. The integrated circuit according to claim 11, wherein the secondA-SRS is received in response to the base station transmitting a requestfor the second A-SRS to the terminal apparatus.